I'm getting 34.8 average out of my 335D, and thats kinda driving normally (i.e. mostly sensibly with the occasional squirt past someone). Have had 42 on a trip oop norf, and had 26 whilst driving like I stole it.

Is that about right?

I measured my 335d on every tank - best was 39.2mpg, worst was 25.0mpg